Electromagnetic wave receiving and amplifying system



May 26, 1925. Y "1,539,464

. F. J. CHAMBERS .zLzc'rnonsns'nc wAvs RECEIVING AND AMPLIFYING SYSTEM Filed D06. 13, 1922 Il kl' l Patented .May 26, I925.

'- UNITED STATES 1,539,464 PATENT OFFICE.

FREDERICK JOHN CHAMBERS, OF LONDON, ENGLAND, ASSIGNOR OF ONE-HALF TO LEONARD ALAN LEGGATT, OF LONDON, ENGLAND.

ELECTROMAGNETIC WAVE RECEIVING AND AMPLIFYING- SYSTEM.

Application filed December 13, 1922. Serial No. 606,583.

To all whom it may concern:

Be it known that I, FREDERICK JorIN' cuit arrangement for use in connection with such tube elements. Y

The principal feature of. the invention consists in the provision of ananode circuit comprising an inductive resistance and two condensers all in series with the anode battery, the anode being connected to the junction point-of the inductive resistance and the condensers while the filament is connected to the junction point of the condensers and anode battery, the outgoing oscillations being led from the terminals of one of said condensers while the incoming oscillations are led directly and independently of the anode circuit tothe terminals of the filament and grid. This circuit is adaptable and may have its constants of such value as to be oscillatory at the lowest frequency while at the same time remaining suitable as regards retro-active effects through the valve, the incoming oscillations are led into a circuit connected between the grid and the filament which circuit is coupled to the anode circuit in the preferred form solely through the valve. In fact this is always the case except in a cascade arrangement where the inductance in the. anode circuit of the second valve may be coupled to the inductance in the anode circuit of the first valve as will be described more fully hereinafter.

In known devices the resistance and the capacity between-the grid and filament of the usual type of valve has barred the possibility of useful oscillation at low radio and audio frequencies and this advantage is achieved by the present invention, more especially due to the insertion of capacity across the valve in series with inductance and reslstance 1n the circuit of the anode battery.

The anode battery is connected through an inductance a resistance or both to the anode. As thevariations of voltage across the condensers will be inversely proportioned to their capacities, one condenser is usually made of considerably greater capacity than the other and-it is from across the terminals of the smaller condenser that the outgoing oscillations are taken. The capacities of the condensers are suitably selected with respect to the inductanceand resistance in the anode circuit in accordance with the particularfuse to which the arrangement is put. v

Such applications of the invention will be better understood by referring to the accompanying drawingsyin which Fig. 1 illustrates the invention as applied to a combined detector and amplifier, with means for making the circuits selective or non-selective as desired, while Fig. 2 shows a modification showing only one thermionic tube element, which is designed to both detect and amplify in itself.

As regards Fig. 1 it should be mentioned that the circuit is designed for various'uses which will be described later.

The thermionic tube elements are shown in the usual conventional form, the filaments being arranged in parallel and fed from a small battery B through .an adjustable resistance AR; The anode battery B is -connected with its negative pole to one side of the filaments and its positive pole to the anodes of the different valves 1, 2 and 3. In the first case through aresistance R and an inductance I and in the second case through a resistance R and an inductance I and in the third case through a telephonic receiver HR. The incoming oscillations which come from an antenna or any other suitable source are applied between the grid and the filament of the first valve. Across the first valve are condensers C 0 in series; across the second valve are two condensers C also in series. The values of the resistances, inductances and con densers vary according as to what the sys tem is'to be used for, being readily chosen by those versed in the art of wireless telegraph and telephone design. Preferably the first valve would be arranged toact principally as a detector, and the secondvalve and third valve as amplifiers, although this is not essential as the first valve could be used as an amplifier, the'sec ond valve as a detector and the third'valve as an amplifier.

The capacity of the condenser G and C should be such-as to offer a' low reactance to the resultant oscillations in the anode circuit of, the first and second valves respectively, whilethe capacity of the condensers 0 should be of'a considerably lower in the modern amplifying valves is an extremely important matter when dealing with audible and even low radio frequencies. The reactance of this condenser should therefore'be in proper relation to the resistance of the grid-filament path, having regard to the degree of damping which is desired. It

is understood of course, that the number of valves is only shown by way of example in Fig. 1 and any other number than three can" be employed as may be desired. 4 The receiver HR in that case would of, course be always connected up in the anode circuit of the last valve of the series. Oscillations applied to the grid of the first valve are not instantly reproduced in similar but amplified form at the grid of the succeeding valve, as such conditionscannot be reached until the expiration of the transitory period during whichtheproportion of energy storage in the several circuit components is auto- 'mat ically readjusted to the lmposed conditions'. Again the induced effects do not cease simultaneously with the applied oscillations, as there must again be a re-distribution of stored energy before the stable conditions are reached. In most known forms of amplifier circuits, these changes are generally accomplished by a compound oscillation containing a number of component frequencies attributablerespectively to the various circuits traversed, butin the present case in view of the simplified circuit arrangements for transient oscillations may be reduced to a simple wave form, and may be arranged to augment desirably the amplification.

I When the trains of applied oscillations are short as for instance in receiving Spark [signals or continuous wave Morse signals on long wave-lengths, the transient oscillations may be extremely important.' According to the values 'of the circuit constants, the amplitude of the transient effects may in such cases be much greater and those 'may persist much longer than the forced effects. I

.pulses give a a positive potential, and' it ."suis w- 3 It is desirable, however, 'forcertain purposes, to suppress the transient cfiects, for reducing, for instance, the-eflects of 1on1c 1rregularities in the "elves or atmospherics, or

pose for which the amplifying apparatus is intended.

As an illustration of the transient phenom-- ena, a simple case will be taken when the grid of the first valve becomes slightly negative on the reception of an impulse. In that case some of the sto'redenergy must be discharged from the field of the inductance I connected to its anode before the anode current can fall to the value determined by the characteristic of the said valve. This en-- ergy will be principally transferred to the. condenser and will set up oscillations of potential between the grid and the filament of the second valve. This efi'ectwill be termed the inductan'ce'efiect. Moreover, if there is an appreciable resistance in the windings of the anode inductance- I as compared with' the internal resistance of the anode filament path, or if resistance, such as R of a similar value be inserted in the anode leads, a certain additional charge must be conveyed to the condensers C 0 in order to raise thedifi'erence of potential between these points to the new value determined by the valve characteristics. This effect will be termed the capacitance effect. On the other hand, in the case of the grid of the first valve becoming slightly positive on the reception of an impulse, as the batterycurrent through the valve will tend to increase, there would be naturally some delay due to-the fact that the field of the inductance has to be first built up. A certain amount of the energy on the condenser "is therefore discharged through the valve. ,This will be referred to as the positiue. efiect. By suitably choosing the constants of the circuit so that the product ofthe resultant capacity of the two condensers'in series and the resistanceof the the valve circuits are preferably adjusted to.

have a natural frequency considerably lower than the applied oscillations, then high trc-' quency oscillations are rectified and may be detected as is shown-for examplejn Fig. 2, the receiver HR being'connected across the condenser 0 Preferably Iis a very large inductance so that the negative-grid imc is large cannot be discharged in the short intervals when the grid is positive, and the result is that the potential on 0 rises during a train of impulses and restores on completion of the train. Of course, the same remarks apply to the first valve of Fig. 1 if this is to detect. The advantage of this kind of rectification over known methods is that the smallest impulse is rectified so that it is not necessary to amplify Weak signals before rectification.

' The following values have been found to give highly satisfactory results. The inductance I henries, resistance Ti -10 ohms, capacity -of condensers C 0 in series 19 farads, valve resistance 3x10 ohms. It will be seen in this example that CR and L/R are both equal to 3x10 seconds which is considerably larger than the duration of any radio frequency oscillation. It will also be recognized that the natural period of this circuit is of audio frequency.

If it is desired to employ a circuit such as shown in Fig. 1 for selectivity to impulses of predetermined frequency or duration, the time constant of the valve circuits may be regulated by inserting non-inductive resistances 1' 1, either inseries with the condensers or as leakage shunts. Alternately grid potentiometers may be employed for this purpose. When selectivity is desired the resistances R, B should be kept low, and the shunt reistances 1' r high. For this reason the switchesS, S 8 s are provided, although if desired adjustable resistances or a number of resistances controlled by separate switches could be employed to give a greater range of adjustment. By this means the time constants of the discharge circuit may be adjusted so asto be long compared with the duration.

of a single impulse. If on the other hand it is not desirable'that the system should be selective, as for. instance in amplifying speech waves, or in designing amplifiers to be effective over a wide range of frequencies, means as above described may be employed to reduce the time constant, but it is not desirable to carry these beyond the point when the time constant of the discharge circuit is comparable with the duration of an individual impulse, unless the requirements are exceptional as for instance, when it is intended to eliminate the transient effects altogether, and employ only the forced effects.

The circuit consisting of the anode inductance, the two condensers and the anode battery in series may be tuned to the impulse frequency or to some multiple of this or a higher frequency if the impulses are of short duration compared with the time impulse between them. The above mentioned inductance may if desired, be that,

which will thus tune thedischarge circuit,

'mitting station.

and for this purpose may be made variable, the condensers may also he made variable if desirable or convenient. For stability condensers C C 0 a may be shunted b high resistance leakage paths. I

One advantage of the construction, ac*.'

cording to the invention is that the possibility of retraction is practically eliminated and if the inductances 1 I are high, battery disturlmnces will be reduced to a minimum. For this reason in audio-frequency work, the inductances l and 1 are provided with iron cores, and the inductance may be as high {IS-30 henries or even higher. If a cascade of three or more valves is connected in the manner described the anode inductanccs may be suitably coupled together, the two'oscillating circuits Will then react upon each other and tend to produce a cumulative effect, the extent of which is affected by the coupling, and the relation between their twonatural frequencies. .In' this manner, according to a further feature of the invention, circuit arrangements may be set up which enable a small impulse applied to the grid of the first valve to bring into play a much larger amount of energy. If therefore, a suitable recording instrument or relay be inserted in the anode circuitof the third or succeeding valve, a

small impulse or succession of small imbetween them. By such an arrangement,

according to the invention, continuous oscillations may be detectedwithout having recourse to the well-known heterodyne method, which consists in superimposing a continuous oscillation of slightly different frequency upon that received'from a trans- In order that the beat fre quency may be varied at will by the operator, the coupling between the circuits may be made variable. two circuits are coupled in order to interact may be that opposed to the generation of continuous oscillations in the well known manner. Clearly the same resultsmay be obtained by an electrical coupling or by the use of resistances.

An audio frequency amplifier can be arranged so as to utilize the surge or transient effects to supplement the forced effects. In

The sense in which the U) this case the resistance R in the anode circuit is comparable with the resistance between the anode and the filament.

r current.

The capacitance efl'ect abovereferred to can be best represented by the following Assumeegzinitial-potential across valve.

R zvalve resistance. a r E L-resistance in. anode circuit,-/ Ezvoltage of anode. battery, then RYIRT,

1 On a negative impulse it will be assumed tiat 1 R changes to R then Thenthe energy involved:

3 and 1 By employing circuit constants which ensure a comparatively low damping co-eflrcient, then charging current of the condens-'- ers C 0 from the battery B will be of an oscillatory nature; and by making the re- I sultant capacitance effect of the condensers quency currents are C ,.c ;in series predominating as regards the inductance efiect, then if a negative-impulse appliedbetween' the-grid and filament persists for sufiicient time, the amplified voltage across the condensers may be nearl doubled; consequently, if the circuit inclu ing B R, I, C, cjstuned to twice thefrequency of the a plied. impulses, the tran sient efii'ects wlllappreciably supplement the forced-- effects. In this way a highly eflicientamplifier isobtained. If high frequency oscillations are applied, this arrange ment serves equally well. as a rectifier, for j the radio frequency currents as referred to previously. 1 I I A second advantageous effect is obtained if the frequency: of the applied audible frethe same frequency as the natural frequency of the amplifier cir-v cuits. This will depend upon the value of the inductance I, and the efi'ect of positive impulses applied to the valve. By using suitably roportioned circuit -components,

-very use ul results can be. obtained with.

speech currents without damping the circuits too highly.

.What I claim and desire to protect by v Letters Patent is.:

1. A receiving arrangement for electrical oscillations comprising a source of electrical.

oscillations, a thermionic valve having a filament, a, grid, and an anode, a circuit connecting said source of electrical-oscillations between said filament and said gr'd, a battery, an oscillatory anode .circult compris ing an inductive resistance, connected between said battery-and said anode, the other terminal of said batterybeing connected to said filament, and two condensers in series connected between said anode and said filament and a receiving device connected across the terminals of one ofsaid condensers 2. A receiving arrangement for electrical oscillations comprising a source of electrical oscillations, a thermionic valve having a filament a grid and an anode, a'circuit connecting said source of electrical oscillations between said filament and said grid, a battery, oscillatory anode circuits comprising an inductive resistance connected between said battery and said anode the other terminal of said battery being connected to said filament, and two condensers 'in series connected between said anode and said'filament, one of said condensers'being of much greater capacity than the other and. a receivin device connected across the terminals o the condenser of least capacity.

3. A receiving arrangement for electrical oscillations comprising a source of electrical oscillations, a each having a filament, a gridand an anode, and a' battery, each of said filaments being connected together and to the negative pole of said batte oscillatory anode circuits comprising in .the anode and positive pole of said battery,

and a number of pairs of condensers con-.

nected between the anodes and filaments of each. valve except the last, the junction plurality of thermionic valves ucta-nces connected between point ,of the condensers being connected to the next valve in the Series and a receiving device connectcdin the anode circuit of said last valve.

4. A receivingarrangement for electrical oscillations comprisingasource of trains of high frequency electrical oscillations, ather- 'mionic valve having a. filament grid and anode, a batter having its negative ter- -,'minal connected to the filament of said valve, an oscillatory anode circuit comprising an inductance between the ositive pole of said battery and said -ano e, two

condensers in series connected between said anode and said filament and a receiving device responsive only to audio-frequency oscillations connectedacross the terminals of one of said condensers, the values of the inductance and condensers being so selected as to give a high inductance or capacitance effeet and a low positive effect so as to enable oscillations of the frequency of the trains of impulses to be detected on said receiving device due to a cumulative change of voltage across its terminals being created by a train of oscillations and dissipated between trains.

5. A receiving arrangement for electrical oscillations comprising a source of electrical oscillations, a thermionic valve having a filament, a grid and an anode, a circuit connecting said source of electrical oscillations between said filament and said grid, a battery, an oscillatory anode circuit comprising an inductive resistance, connected between said battery and said anode, the other terminal of said batterybeing connected to said filament, and two condensers in series connected between said anode and said filament and a receiving device connected across the terminals of one of'said condensers, the value of said inductive resistance and the capacity of said condensers being so chosen'that the frequency of the anode circuit is comparable with the frequency of the received oscillations so that these can be amplified without change.

6. A receiving arrangement for electrical oscillations, a thermionic valve having a fila ment, a grid and an anode, a circuit connecting said source of electrical oscillations between said filament and said grid, a battery, an oscillatory anode circuit comprising an inductive resistance, connected between said battery and said anode, the other terminal of said battery being connected to said filament, and two condensers in series connected between said anode and said filament and a receiving device connected across the terminals of one of said condensers the valuev of the resistance of said inductive resistance being comparable with the resistance between the anode and the filament and the inductance effect is low compared with the capacitance. i

7. A receiving arrangement for electrical oscillations comprising a source of electrical oscillations, a thermionic valve having a filament a grid and an anode, a circuit connecting said source of electrical oscillations between said filament and said grid, a battery, an oscillatory anode circuit comprising an inductive resistance, connected between said battery and said anode, the other terminal of said battery being connected to said filament, and two condensers in series connected between said anode and said filament and a receiving device connected across the terminals of one of said condensers, the frequency "lations comprising a number of valves arof the valve circuits being adjusted to be equal to or a multiple of that of the received oscillations.

J 8. A receiving circuit for electrical oscilranged in cascade with the filament connected together in which the anode circuits for two valves include an inductance whilebetween the anode and the filament of each valve are two condensers in series, the junction point of the condensers ofsaid valves being connected to the grid of the next succeeding valve, characterized in that the anode circuits of the two valves are so arranged as to exert a mutual effect on each other. 7

9. A receiving circuit for electrical oscillations comprising a number of valves arranged in cascade with the filaments con-. nected together in which thevanod'e circuits for two valves include an inductance While between the anode and the filament of each valve are two condensers in series, the junction point of the condensers of said valves being connected to the grid of the next sueceeding valve, characterized in that the anode circuits of the, two valves are so arranged as to exert a mutual eifect on each other, and are tuned to' the same frequency as the applied oscillations whereby continuous oscillations may be detected by means of beats, 4

10. A receiving circuit for-electrical oscillations comprising a'number of valves arranged in cascade with the filamentsconnected together in which the anode circuits or two valves include an inductance while between the anode and the filament of each valve are two condensers in series, the junc tion point of the condensers of said valves being connected to the grid of the next succeeding valve, characterized in that the anode circuits of the two valves are so arranged as to exert a mutual effect on the other, being closely coupled together adjusting means'being provided whereby the degree of coupling can be varied at will.

11. A receiving arrangement for electrical oscillations comprising a source of electrical oscillations, a thermionic valve having a filament a grid and an anode, a circult connecting said source of electrical oscillations between said filament andsaid grid, a battery, an oscillatory anode circuit comprising an inductive resistance, connect- 1'20 ed between said battery and said anode, the other terminal of said battery being connected to said filament, and two condensers I in series connected between said anode and said filament and a receiving device connectoscillations, a thermionic valve having a filament a grid and ,an anode, a circuit connecting said source of electrical oscillations between said filament and said grid, a battery, an oscillatory anode circuit comprising an inductive resistance connected between said battery and said anode the other terminal of said battery being connected to said filament, and two condensers in series connected between said anode and said filament, one of said condensers being of much greater capacity than the other and a receiving 'grid and filament of the second valve.

In testimony whereof I affix my signature in presence of two witnesses.

FREDERICK JOHN CHAMBERS. Witnesses:

FRANK I. HALEY, LEONARD R. MYRAM. 

